There has been proposed a laser printer including a toner replenishment method for replenishing a developing device from a toner cartridge with toner (for example, see JP-A-9-319202).
In the laser printer including the toner replenishment method, the toner cartridge is configured attachably to and detachably from an inside of the developing device. In a state of attaching the toner cartridge to the developing device, an inside of the toner cartridge communicates with an inside of a developing chamber of the developing device by a toner supply opening provided in a center in a width direction of the toner cartridge and by toner suction openings provided on both sides of the supply opening. An agitator for supplying toner from the toner supply opening to the inside of the developing chamber while agitating the toner is disposed inside the toner cartridge. Inside the developing chamber, a developing roller, a supply roller for supplying toner to the developing roller, and an developer transport member for transporting toner are arranged. The toner supplied from the toner supply opening to the inside of the developing chamber is transported from the toner supply opening toward each of the toner suction openings on either side of the supply opening of the toner cartridge by the developer transport member of the developing chamber. Then, the toner is returned from each of the toner suction openings to the inside of the toner cartridge. Consequently, the toner can be deposited uniformly along the whole supply roller while the toner circulates between the toner cartridge and the developing chamber, and the toner is prevented from being retained in a part of the inside of the developing chamber.